Introduction and Calculation Methods of Boiler Efficiency
What is boiler efficiency
It is a well known fact that the initial cost of boiler is a small part of total costs associated with the boiler over its lifetime. In the operational life of a boiler, major costs arise out of the fuel costs. Ensuring efficient operation of boiler is critical to optimize the fuel costs.
Boiler efficiency is a combined result of efficiencies of different components of a boiler. A boiler has many sub systems whose efficiency affects the overall boiler efficiency. Two kinds of efficiencies which finally decide the boiler efficiency are combustion efficiency and thermal efficiency. Apart from these efficiencies, there are some other losses which also play a role while deciding the boiler efficiency and hence need to be considered while calculating the boiler efficiency.
Calculation methods of boiler efficiency
The overall boiler efficiency depends on many more parameters apart from combustion and thermal efficiencies. These other parameters include ON-OFF losses, radiation losses, convection losses, blow down losses etc. In actual practice, two methods are commonly used to find out boiler efficiency, namely direct method and indirect method of efficiency calculation.
This method calculates boiler efficiency by using the basic efficiency formula-
η=(Energy output)/(Energy input) X 100
In order to calculate boiler efficiency by this method, we divide the total energy output of a boiler by total energy input given to the boiler, multiplied by hundred.
Calculation of direct efficiency-
E= [Q (H-h)/q*GCV]*100
Q= Quantity of steam generated (kg/hr)
H= Enthalpy of steam (Kcal/kg)
h= Enthalpy of water (kcal/kg)
GCV= Gross calorific value of the fuel.
The indirect efficiency of a boiler is calculated by finding out the individual losses taking place in a boiler and then subtracting the sum from 100%. This method involves finding out the magnitudes of all the measurable losses taking place in a boiler by separate measurements. All these losses are added and subtracted from 100% to find out the final efficiency.